The present invention relates to an improved method of completing subterranean zones. More specifically, the present invention provides techniques for performing completions in unconsolidated formations to thereby eliminate the need for expensive high-density completion brines and also reduces/eliminates drilling/workover rig requirements for completion operations.
The methods described in this patent may be utilized to perform more productive well completions at significantly reduced costs.
Dual-screen assemblies and Frac Packing techniques are known in the art and have been utilized for oil and gas well completions for a number of years. Exemplary embodiments of dual-screen assembly techniques techniques are taught in my previous U.S. Pat. No. 5,722,490, issued Mar. 3, 1998, which is hereby incorporated herein by reference. My previous patent discloses methods for increasing the production rate from a cased well that might otherwise produce solids through perforations during production. In accord with the methods presented in my previous patent, a gravel pack screen is placed in the well along with equipment in the tubing string to control flow from inside to outside the tubing below a production packer. The rig used for handling the tubing string may then be released from the well. The well is then hydraulically fractured. If the well is producing from a high permeability zone, then the hydraulic fracture is preferably formed with a tip screen-out technique. The method can also be used in a well already containing production tubing without moving a rig onto the well to remove the tubing from the well and can be used in a well not yet perforated by adding tubing-conveyed perforating apparatus below the screen.
It is well known by those of skill in the art that oil and gas wells are drilled with a fluid, called drilling mud, which normally has a density greater than water. Typically, after well logs are run to confirm that commercial zones of hydrocarbons have been encountered along the wellbore, steel casing of various sizes is run into the well. The casing is cemented in the wellbore utilizing cementing techniques well known in the art, and then the completion phase of the well commences.
In many areas of the world, the drilling fluids utilized during drilling may permanently damage the pay zone formation adjacent the wellbore in a manner that reduces the potential production of oil and gas. For this reason, a solids-free completion fluid having a selected density is frequently used to displace the drilling fluid from the wellbore as an initial part of the well completion process. Use of a suitable completion fluid is particularly desirable in high permeability, and unconsolidated, formations found throughout the world.
High-density completion fluids are often necessary in conventional well completions to maintain sufficient hydrostatic pressure to control the bottom hole pressures of the producing zones for relatively higher pressure producing zones. However, high-density completion brines can be very expensive, dangerous to field personnel, and often times damaging to the producing zones. Zinc bromide completion fluid, in the density range of 14-20 pounds per gallon, is particularly expensive and damaging. Nonetheless zinc bromide completion fluid is commonly utilized in the prior art despite these known deficiencies because of a lack of more suitable alternatives. Those of skill in the art have focused upon methods and techniques to eliminate the use of zinc bromide completion fluids for many years. Thus, the present invention provides innovative and low-cost solutions to quite significant technical problems encountered for many years by those of skill in the art of well completions.
The technique of Frac Packing a production zone to bypass the damage created by the drilling fluid, and cementing operations, has become the prevalent completion technique utilized for unconsolidated formations. Frac Packing has replaced gravel packing, and high-rate water packing, as the most efficient means to produce these types of pay zones, without the production of formation sand. Normally, the Frac Pack technique results in the highest completion rates, with the lowest drawdown at the formation/wellbore interface.
The elimination, or time reduction, of the use of a drilling rig or workover rig, or other type of well intervention device, e.g., a coiled tubing unit, has a significant effect on the cost of completing an oil or gas well. The rig time required to perform a conventional well completion on unconsolidated zones can be extensive and costly. As used herein a rig is a device with a high lifting capacity capable of lifting an entire string of tubing or pipe, which may have a length of over several thousand feet in length. The rig also includes pipe-handling means for breaking/making pipe connections as the tubular string is removed and/or inserted into the wellbore. Various types of rigs may include jack-up rigs, masts, workover rigs, upright derricks with traveling blocks, drilling rigs, and the like including associated pipe-handling devices. The cost of the rig, coupled with the use of high-density completion brine, can easily result in a non-economical operation. By eliminating or reducing these costs in accord with the techniques of the present invention, many oil and gas wells may now be profitable to drill and complete that otherwise would not be profitable. Moreover, the present invention has the potential to significantly increase profitability of otherwise profitable wells.
Various inventors have attempted to solve problems related to those discussed above as indicated by the following patents:
U.S. Pat. No. 6,095,245, issued Aug. 1, 2000, to M. J. Mount, discloses a repositionable apparatus for perforating and gravel packing an underground well which uses gravity or other means to reposition the apparatus instead of a conventional wireline or work string attached to a rig. Perforating and packing can be accomplished without a rig after the apparatus is initially placed and set in the well. One embodiment of the inventive apparatus uses a perforating gun assembly, a connected ported sub above the gun assembly, a translating annulus packer above the ported sub, a circumferential screen located above the packer, blank pipe connected above the screen, an openable port above the blank tubular pipe, and a second translating annulus packer attached to the blank tubular.
U.S. Pat. No. 6,253,851, issued Jul. 3, 2001, to D. E. Schroeder, discloses method of completing a well that penetrates a subterranean formation and more particularly to a method for screen placement during proppant packing of formation perforations or fractures created by hydraulic fracturing techniques. The top of the screen is placed at a sufficient distance below the top of the perforations such that the frac pack pumping rate does not bridge off at the top of the screen when the frac pack is being pumped.
U.S. Pat. No. 6,003,600, issued Dec. 21, 1999, to Nguyen et al., discloses methods of completing unconsolidated subterranean zones penetrated by wellbores. The methods basically comprise the steps of placing a slotted liner in the zone, isolating the slotted liner and the wellbore in the zone, injecting a hardenable resin composition coated particulate material into the zone by way of the slotted liner and then causing the hardenable resin composition to harden whereby the particulate material is consolidated into a hard permeable uniform mass.
U.S. Pat. No. 5,115,860, issued May 26, 1992, to Champeaux, et al., discloses an apparatus for setting a gravel pack in an oil well through tubing situation and includes the steps of running a tool body into the well using an electric wireline deployment. The tool body is precisely positioned relative to the surrounding casing, and radially extending members attached to the tool are used to extend from the tool body and center the tool body in the well bore. Sand control media such as a gravel pack is disposed in the well annulus circumferentially about the tool body using a dump bailer. The use of radially extending members allows the tool body to pass through restricted diameter areas such as production tubing, fittings, nipples, pressure control device, packers, valves and the like.
U.S. Pat. No. 5,373,899, issued Dec. 20, 1994, to Dore"" et al., discloses an invention for controlling a well during completion by first running a sealable well completion tool and string downhole from the surface and isolating a productive interval near an oil or gas formation from the remainder of the wellbore. The drilling or other fluid in the interval is displaced from the interval under control by a non-damaging fluid. Using a pressure source from the surface, the non-damaging fluid is pressurized and circulated to move the gravel to the formation face by fluid entrainment. After the gravel is separated from the entraining fluid to form a gravel pack, the oil or gas formation may now be produced through the gravel pack.
U.S. Pat. No. 5,865,252, issued Feb. 2, 1999, to van Petegem et al., discloses a one-trip production zone perforation and proppant fracturing operation carried out using a workstring-supported perforation gun lowered into a casing nipple located in the production zone. Firing of the gun creates spaced apart aligned sets of perforations extending outwardly through a side wall portion of the workstring, the nipple, the surrounding cement, and into the production zone, after which the gun falls into and is retained in an underlying gun catcher portion of the workstring. While an overpull force is maintained on the workstring above the perforations, a proppant slurry is pumped down the workstring, out its sidewall perforations, and outwardly through the aligned perforation sets formed in the nipple, cement and production zone. After stimulation of the production zone, the workstring and the spent perforation gun that it retains are pulled up, with the upwardly moving workstring positioning a sliding closure device inwardly over the perforations to isolate the stimulated production zone until the well is readied for production. Illustrated alternate embodiments include the use of a low debris casing gun in place of the drop-off type perforating gun, the use of pre-formed wide wall perforations in the workstring side wall, and a one-trip perforation and production flow creating method in which the production zone stimulating step is eliminated.
U.S. Pat. No. 5,975,205, issued Nov. 2, 1999, to J. V. Carisella, discloses a through-tubing gravel packing operation utilizing inflatable packing elements and a flow cross-over assembly which selectively opens flow ports for effecting steps in the gravel packing operation and which further provides concentric flow paths through the cross-over assembly for transmitting fluid pressure to valving means and the interior of the packing element or elements to move them to set and sealed condition, whereby the outer diameter of the inflatable element in the sealed condition may preferably expand to at least twice the outer diameter of such element in the initial or run-in condition, for the sequential setting thereof while also transmitting a variation in the pressured fluid to actuate a valve for circulation of the gravel packing fluid exterior of the assembly and for permitting return of fluids through the assembly without the gravel. When plural packing elements are incorporated, the device includes valving components which permit the setting of the lower or sump packer prior to the setting of the gravel pack packer as well as the opening of the gravel packing sleeve valve and a valving component within the gravel packing screen for circulation. The device is mechanically manipulatable after the setting operation for various steps in gravel packing of a subterranean well through tubing introduced through production tubing disposed through a Christmas tree.
U.S. Pat. No. 4,378,845, issued Apr. 5, 1983, to Medlin et al., discloses a sand control method wherein high viscosity, high sand concentration, fracturing fluids are pumped through sets of vertically oriented perforations in borehole casings located in unconsolidated or loosely consolidated pay zones. Various techniques are utilized to insure that sand fills disposed on either side of the borehole casing cover and substantially overlap each borehole casing perforation set. Procedures are then followed to bring the well into production without washing out the sand fills in these areas, whereby the resulting perforation-sand fill configurations effectively control sand production from the treated zone.
U.S. Pat. No. 5,329,998, issued Jul. 19, 1994, to King et al., discloses a combination perforating/gravel pack assembly which includes a crossover circulation tool, a gravel pack screen, gravel pack accessories and a perforating gun which are interconnected by tubular flow conductors. External seals are located at longitudinally spaced locations along the upper end of the flow conductor string, above the gravel pack accessories and screens. External seals are also located at longitudinally spaced locations along the lower end of the flow conductor string, intermediate the screen and the perforating gun assembly. After crossover and reverse circulation are established, gravel slurry is pumped through an inner service string into the production annulus between the screen and the perforated casing. The slurry liquid is returned through a tell-tale screen upwardly through the washpipe and circulation tool, where it crosses over for return flow to the surface through a bypass annulus between the inner service string and the upper flow conductor seal assembly.
U.S. Pat. No. 5,845,712, issued Dec. 8, 1998, to C. F. Griffith, Jr., discloses apparatus and associated methods for performing operations within a subterranean well to overcome many disadvantages associated with perforating and fracturing and/or gravel packing by making a single trip of a work string into the well. In a preferred embodiment, a method of producing fluids from a formation intersected by the well includes the step of setting a packer having a relatively large seal bore formed therethrough in the well before running the work string into the well. After the formation is perforated, the work string is displaced to position a seal assembly on the work string in the seal bore, thereby displacing the perforating guns through the packer, positioning a screen opposite the perforated formation, and enabling performance of gravel packing operations thereafter.
U.S. Pat. No. 5,623,993, issued Apr. 29, 1997, to Van Buskirk et al., discloses a wellbore to be treated which is at least partially obstructed with a partition or obstruction member. A fluid slurry of an aggregate mixture of particulate matter is pumped into the wellbore adjacent the partition or obstruction member. The aggregate mixture of particulate material contains at least one component of particulate material, and each of the at least one particulate material components has an average discrete particle dimension different from that of the other particulate material components. Fluid pressure then is applied to the aggregate material and fluid is drained from the aggregate material through a fluid drainage passage in the partition or obstruction member. The fluid pressure and drainage of fluid from the aggregate mixture combined to compact the aggregate mixture into a substantially solid, load-bearing, force-transferring, substantially fluid-impermeable plug member, which seals a first wellbore region from fluid flow communication with a second wellbore region. The plug member is easily removed from the wellbore by directing a high-pressure fluid stream toward the plug member, thereby dissolving or disintegrating the particulate material of the plug member into a fluid slurry, which may be circulated out of or suctioned from the wellbore.
U.S. Pat. No. 5,954,133, issued Sep. 21, 1999, to C. M. Ross, discloses methods of completing wells utilizing wellbore equipment positioning apparatus to provide repositioning of sand control screens and perforating guns without requiring movement of a packer in the wellbore. In a preferred embodiment, a well completion method includes the steps of lowering a packer, positioning device, sand control screen, and perforating gun into a well, perforating a zone intersected by the wellbore, expanding the positioning device, and positioning the sand control screen opposite the perforated zone.
U.S. Pat. No. 6,059,033, issued May 9, 2000, to Ross et al., discloses apparatus for completing a subterranean well and associated methods to provide economical and efficient well completions. In one described embodiment, a well completion apparatus includes a packer which is settable by application of a compressive axial force thereto. The packer sealingly engages a wellbore of the well when set therein, but does not anchor to the wellbore. The apparatus further includes a screen and an attachment device. The attachment device permits the apparatus to be attached to another packer previously set and anchored within the wellbore.
U.S. Pat. No. 6,138,755, issued Oct. 31, 2000, to R. Swartwout, discloses a method for enhancing the compatibility of a zinc-brine completion fluid with a fracturing fluid. Test samples of selected completion fluids are combined with test samples of selected fracturing fluids to form an admixture. The parameters of incompatibility between the completion fluid and the fracturing fluid are analyzed and identified. The parameters or indicia of incompatibility identified can be precipitation, emulsification and/or an increase in viscosity. The zinc brine completion fluid is then blended with additives to remove these parameters of incompatibility. The additives can be selected from a group comprising hydrochloric acid, hydrobromic acid, acetate salts, citrate salts, and surfactants. At the well site, the altered zinc brine completion fluid is pumped in to displace drilling fluids in the wellbore before pumping in fracturing fluid. Additional altered brine completion can follow the fracturing fluid into the wellbore. Commingling of the altered zinc brine completion fluid with fracturing fluid in the wellbore or the formation can occur without substantial damage to the formation.
U.S. Pat. No. 6,206,100, issued Mar. 27, 2001, to George et al., discloses a system and method for perforating and gravel packing a wellbore casing in a single trip into the wellbore comprising a gravel packer assembly having a production screen and at least one packer. A perforating apparatus is connected to the gravel packer assembly, wherein the perforating apparatus is detachable from the gravel packer assembly after the system is placed in the wellbore and before a detonation of the perforating apparatus. A tool is disclosed having at least one casing engaging slip segment, wherein the tool is matable with the perforating apparatus and is settable in the wellbore casing.
U.S. Pat. No. 6,220,353, issued Apr. 24, 2001, to Foster et al., discloses a full bore set down tool assembly that provides a housing attached to a packer in a wellbore aligned with the production zone. A service tool of the tool assembly is attached to a tubing string extending to the surface and is adapted for selective, removable attachment to and positioning within the housing. The tool assembly defines a downstream flow path and a return flow path when the service tool is attached to the housing. A ball valve that is selectively shiftable from the surface opens and closes the return flow path to define a circulate position and a squeeze position. The housing, service tool, and ball valve also define a reverse position. The tool assembly facilitates gravel packing of the annulus between the wellbore casing and the service string including the tool assembly.
U.S. Pat. No. 6,230,802, issued May 15, 2001, to M. Duhon, discloses an apparatus for use in gravel packing a well which includes a tool body adapted to be lowered into the well, a screen coupled to the tool body, and a resilient member coupled to the screen. The apparatus is placed at a selected position in the well, and sand control media is disposed between the screen and the well while the resilient member is periodically excited to vibrate the screen.
U.S. Pat. No. 6,241,013, issued Jun. 5, 2001, to W. J. Martin, discloses a one-trip squeeze pack system which has a unique service seal unit design using concentric tubing, with the inner tubing an extension of the traditional wash pipe and is later used as the production tubing. The inner tubing contains a ported sub which can be isolated in various positions within the outer tubing by way of seals located above and below the ported sub. This seal unit is raised and lowered on the production string and isolated at various positions in order to accomplish setting the packer, running a packing job, reversing out packing fluid, and receiving production fluids.
U.S. Pat. No. 5,505,260, issued Apr. 9, 1996, to Anderson et al., discloses a single trip system for placing perforating apparatus and sand control equipment in a wellbore. This system includes a casing string equipped with extendible pistons and a pumpable activator plug for extending the pistons. Additionally, this system utilizes a single gravel-pack and completion tool string. Further, this system includes a means for opening the extendible pistons to fluid flow.
U.S. Pat. No. 5,492,178, issued Feb. 20, 1996, to Nguyen et al., discloses fracturing, frac-pack, and gravel packing procedures which utilize a treating composition comprising a carrier fluid and a particulate blend. The particulate blend consists essentially of a large particulate material and a small particulate material. The large particulate material consists essentially of particles smaller than about 4 mesh but not smaller than about 40 mesh. The small particulate material consists essentially of particles smaller than about 16 mesh but not smaller than about 100 mesh. The small particulate material is present in the particulate blend in an amount in the range of from about 5% to about 60% by weight based on the amount of the large particulate material present in the particulate blend. A prepacked screening device including a large particulate/small particulate blend of the type just described is also provided.
U.S. Pat. No. 6,176,307, issued Jan. 23, 2001, to Danos et al., discloses that after installing an inventive tool attached to production tubing in a well, the well can be gravel packed without the use of a well intervention unit. The tool isolates a productive interval and diverts tubing-conveyed sand slurry towards an annular location by means of a port and an openable passageway restrictor. The entraining fluid component of the diverted sand slurry in the annular location is allowed to re-enter the production tubing through a first screen while the separated sand drops to the annular location to be packed in an axial direction. Rupture of a plug then allows the separated sand to be packed in an axial direction.
The above cited prior art does not disclose how to perform a Frac Pack in a high pressure production zone utilizing low weight completion fluids that do not in themselves provide a sufficient downhole hydrostatic pressure to control the production zone while also reducing or eliminating rig time for completion operations to thereby improve well performance and lowers costs. Consequently, those skilled in the art will appreciate the present invention that addresses these and other problems.
The present invention provides methods of completing oil and gas wells in subterranean unconsolidated zones with high completion efficiency, and reduced costs, utilizing readily available equipment. The improved methods eliminate the need for high-density, and high cost, completion fluids. The improved methods reduce drilling rig costs and other costs. The improved methods lower the various costs of deploying a dual-screen assembly in the well. In wells without a high deviation, or hole angle, a preferred method of the present invention also eliminates the cost of coiled tubing equipment. Many wells have multiple producing zones, and a preferred embodiment of this invention allows for the re-completion of zones in the wellbore to performed, in many cases, completely without the use of a workover rig.
In a new well, casing is run into the well and cemented in place. With the rig on location, a cast iron bridge plug may be run into the well with electric line, or on drill pipe, and set a depth below the lowest-most zone to be completed. The drilling fluid used to drill the well is then displaced out of the wellbore with a low-density well completion fluid such as potassium chloride. A production packer is run in the well on electric line or drill pipe and set at a depth approximately 100 feet above the uppermost commercial zone in the wellbore. Production tubing of various size is run into the well and the seal assembly near the bottom of this production tubing is set into the bore of the production packer. The wellhead tree is installed, and two sub-surface safety valves may preferably be placed in the production tubing string at a specified depth. In a preferred embodiment, the rig can then be moved off the well, and the completion operations initiated according to the present invention. In an offshore environment, a lift boat can be used for the remainder of the well completion. In some cases offshore, the well to be completed is tied back into a producing platform. If the platform has adequate deck space, and weight requirements, the initial and subsequent completions can be performed on the production platform.
Normally, a wellhead isolation tool is installed to eliminate pressure and erosion from the wellhead tree during the Frac Pack operation. An electric line logging and perforating unit is rigged up on the lift boat, or the platform, on an offshore well. Correlation and cased hole production logs are run, and then the zone is perforated through-tubing with a perforating device run on the electric line. The perforating device is detonated after a predetermined amount of pressure is placed on the well to compensate for the differential between the hydrostatic pressure of the well completion fluid such potassium chloride brine and the bottom hole pressure of the zone. This pressure is maintained on the well at the time of perforating gun detonation to prevent the zone from producing any formation sand into the wellbore. By manipulating the sub-surface safety valves with respect to the position of the perforating gun in the wellbore, pressure is maintained on the well as the wireline guns are extracted such that the bottom hole pressure adjacent zone is slightly overbalanced. In a similar manner of operating the sub-surface safety valves, sufficient bottom hole pressure is maintained as the dual-screen assembly is made up and run into the well. This assembly is run into the well and placed on top of the bridge plug by use of the electric line, braided line, or coiled tubing. A disconnect device is run at the top of the dual-screen assembly, and the assembly is separated from the deployment line, or coiled tubing.
With a wellhead isolation device made up on the top flange of the wellhead tree, equipment to perform the Frac Pack/gravel pack operation is mobilized to the well. In the case of a Frac Pack, the required fluids, additives, and proppants are pumped down the production tubing and into the zone, traveling through the casing/dual-screen annulus into the perforations. The displacement of the Frac Pack is preplanned to leave a few barrels of frac fluid and proppant above the top of the vent screen, which is at the upper part of the dual-screen assembly. As soon as the Frac Pack is completed, the zone pressure is utilized wash out or carry the excess proppant/slurry above the top of the vent screen out of the well by back flowing the well. In the case of some wells, particularly in the case of low bottom-hole pressure zones and highly deviated wellbores, coiled tubing may be required to wash out the excess proppant. The well, or zone, can then be put on production.
In the case where a well has a number of potential zones, the method of the present invention is utilized first on the lowest zone in the wellbore. After the lowest zone is depleted, or no longer produces oil and/or gas at a commercial rate, equipment is mobilized on a lift-boat, or to the production platform, to perform a re-completion on the next highest zone in the well. A through-tubing bridge plug is run on electric line, and set at a pre-determined depth. Ten to fifteen feet of cement is dump bailed on top of the bridge plug, the plug tested, and the zone is perforated with a relatively low density completion fluid in the wellbore, such as potassium chloride, with additional pressure applied to the well as discussed above such that the hydrostatic pressure adjacent the new production zone is slightly overbalanced with respect to the formation pressure. Other steps in the preferred method for the remainder of the completion may be identical to that described hereinbefore for the lowest zone of the new well. As each zone is depleted, the same or similar procedure is used for the re-completions.
Accordingly, the present invention provides a method of completing a well with one or more potential production zones which may comprise one or more steps such as, for instance, filling the wellbore with a completion fluid having a density such that a hydrostatic pressure of the completion fluid created within the wellbore adjacent the first production zone is less than the first production zone formation pressure, installing a production packer preferably above the one or more production zones, installing production tubing within the well with a rig such that a bottom end of the production tubing is preferably positioned above the one or more production zones, providing the production tubing with at least one subsurface valve positioned therein, moving the rig off the well, running a perforating gun into the well, applying an applied pressure to the wellbore such that a total pressure of the hydrostatic pressure and the applied pressure in the wellbore adjacent the first production zone is greater than the first production zone formation pressure, perforating the wellbore adjacent the first production zone, pulling the perforating gun above the at least one subsurface valve, closing the at least one subsurface valve to maintain the total pressure in the wellbore adjacent the first production zone, running a screen assembly into the wellbore above the valve while the valve remains closed, opening the at least one subsurface valve, positioning the screen assembly in the wellbore adjacent the first production zone, and pumping fracturing slurry around the screen assembly and into the first production zone with a sufficient pressure to fracture the first production zone.
Other steps may further comprise removing excess components of the fracturing slurry from the wellbore without use of coiled tubing such as by utilizing the first production zone formation pressure to create fluid flow within the wellbore for removing excess components of the fracturing slurry from the wellbore.
When the first production zone is no longer economical to produce, the method may further comprise completing upper production zones without the need for bringing a workover rig back onto the well. This embodiment of the invention may comprise steps such as plugging off the first production zone at a well depth below the second production zone and above an uppermost perforation of the first production zone, filling the well with a second completion fluid which may have a density such that a hydrostatic pressure of the second completion fluid created within the wellbore adjacent the second production zone is less than the second production zone formation pressure, perforating the second production zone without use of the workover rig, installing a second screen assembly adjacent the second production zone without use of the workover rig, and/or pumping fracturing slurry around the second screen assembly and into the second production zone with a sufficient pressure to fracture the second production zone.